High frequency electron discharge devices and wave permeable windows



Aug. 29, 1967 F. o. JOHNSON HIGH FREQUENCY ELECTRON DISCHARGE DEVICESAND WAVE PERMEABLE WINDOWS 2 Sheets-Sheet 1 Filed Feb. 27, 1964.

km mOEa 29, 1957 F. o. JOHNSON 3,339,102

HIGH FREQUENCY ELECTRON DISCHARGE DEVICES AND WAVE PERMEABLE WINDOWSFiled Feb. 27, 1964 2 Sheets-Sheet Fla :0 46

ASPECT RATIO (A/B) N N '9 6.6 714 8.2 910 93 aole mzouemcflec) INVENTOR.FLOYD O. JOHNSON ATTORNEY United States Patent 3 339,102 HIGH FREQUENCYELECTRON DISCHARGE DEVICES AND WAVE PERMEABLE WINDOWS Floyd 0. Johnson,Mountain View, Calif, assignor to Varian Associates, Palo Alto, Calif.,a corporation of California Filed Feb. 27, 1964, Ser. No. 347,911 4Claims. (Cl. 315-3) ABSTRACT OF THE DISCLOSURE Improvements in both highpower electromagnetic wave permeable self-resonant window structureswith respect to improved freedom from ghost modes inducing undesirablethermal expansions and contractions and improved electrical breakdowncharacteristics are achieved by constructing the self-resonant window asa honeycomb (a window having a plurality of voids, bores, substantiallyblanketing a cross-sectional portion of the window taken along a planethrough the window transverse to the longitudinal or thickness dimensionof the window) window of either a singlar or composite type.

This invention relates in general to high frequency electron dischargedevices and more particularly to improved high frequency electrondischarge devices and improved wave permeable window assemblies.

High frequency electron discharge devices such as klystrons, travelingwave tubes, magnetrons, linear accelerators and so forth, are constantlybeing improved in relation to their power output capabilities. At thepresent time, extensive research and development is underway in anattempt to generate average microwave powers in the regions of hundredsof kilowatts and above and peak mircowave powers in the regions of onemegawatt and above. Such investigations have shown that a severelimitation on such high power devices is the vacuum-sealed wavepermeable window assembly of said devices. Window failures haveconstantly been observed due to a variety of causes such as thefollowing: mechanical breakage due to such factors as differentialthermal expansions occurring within the wave-permeable window itselfunder high power operating conditions; electrical breakdown within thewindow itself or in the surrounding waveguide regions which are adjacentthereto which is essentially caused by excessively high local electricfields; breakdown and erosion due to electron bombardments by highvelocity electrons impacting on the window surfaces due to the localizedelectromagnetic fields in the region of the window; thermal expansionsand contractions due to localized spurious resonances such as ghostmodes occurring within the vicinity of the window itself and building upto extremely high power levels only within the vicinity of the window.Other adverse conditions occurring in microwave windows areelectromagnetic reflections due to abrupt impedance discontinuities andmultipactor effects.

Typical examples of relatively high and high power wave-permeablevacuum-tight windows for electron discharge devices are to be found inU.S. Patent 2,958,834, by R. S. Symons et al.; US. Patent 2,698,421, by.T. Kline et al.; US. Patent 2,929,035, by L. M. Winslow et al.; US.Patent 2,786,185, by T. D. Sege et al.; US. Patent 3,058,- 074, by J. F.Kane; US. Patent 2,930,008, by A. S. Walsh; U. S. Patent 2,990,526, byE. I. Shelton, Jr.; US. Patent 2,869,086, by T. P. Curtin et al. Theaforementioned US. patents are cited as illustrative of typicalmicrowave wavepermeable windows for electron discharge devices. In eachcase, the aforementioned wave-permeable windows depicted in the abovecited patents are susceptible when operated at high power to breakdownfor the reasons set 3,339,102 Patented Aug. 29, 1967 forth herein above.The aforementioned waveguide windows set forth in the US. patents arethought to represent a wide spectrum of windows suitable for variableapplications, bandwidths, power outputs and so forth. My copendingapplication, U.S. Ser. No. 316,865, filed Oct. 17, 1963, entitled,Waveguide Window and Devices using Same, and assigned to the sameassignee as the present invention is illustrative of other typical highpower waveguide window configurations. It is thought that in each of theabove illustrative examples that the waveguide windows set forth thereinmay advantageously benefit from the teachings of the present inventionas will be set forth in detail hereinafter.

The present invention, through the utilization of a novel honeycomb, ofeither a singular or composite nature, wave-permeable window techniqueprovides an overall improvement in high power window strength whilesimultaneously rendering said wave-permeable windows less susceptible tobreakdown and consequent destruction due to spurious resonant modesotherwise termed ghost modes therein and due to other casual factorssuch as set forth herein. A honeycombed structure is herein defined asone having a plurality of voids, bores, etc., substantially blanketing acrosssectional portion of said structure taken along a plane throughsaid structure transverse to the longitudinal or thickness dimension ofsaid structure. The present invention furthermore provides means forcooling the aforementioned novel electromagnetic wave-permeable windows.The present invention, through the utilization of a singular orcomposite wave-permeable window as sembly (of honeycomb nature), furtherprovides improved breakdown characteristics due to electron bombardmentin certain specific configurations or embodiments as well as improvedproperties with regard to electric field breakdown. The utilization of ahoneycomb singular or composite window according to the teaching of thepresent invention reduces the dielectric constant of the window and atthe same time permits an increase in the thickness of the window whichresults in increased strength while simultaneously shifting resonantghost modes up in frequency to thereby reduce the probability of windowbreakdown due to excitation of said resonant ghost modes in the passbandof the particular window design under consideration. The presentinvention further provides means for providing built-in impedancetransformation within the window itself as well as means for reducingmultipactor effects.

It is therefore an object of the present invention to provide highfrequency electron discharge devices with means for improving the powertransmission capabilities therefore while simultaneously providing morespurious mode free transmission characteristics.

A feature of the present invention is the provision of a high frequencyelectron discharge device with an improved wave-permeable vacuum-sealedwindow assembly.

Another feature of the present invention is the provision of a highfrequency electron discharge device having improved wave-permeablevacuum-sealed window assembly.

Another feature of the present invention is the provision of ahigh-frequency electron discharge device having improved wave-permeablevacuum-sealed transmission means therefore, wherein said improvedwave-permeable vacuum-sealed transmission means comprise a honey-combwave-permeable window of ,a singular or composite nature.

Another feature of the present invention is the provision of arectangular waveguide having secured therein in a vacuum-sealedrelationship, a rectangular electromagnetic wave-permeable honeycombwindow, said window of a composite or singular structure.

Other features and advantages of the present invention will become moreapparent upon perusal of the following specification taken inconjunction with the accompanying drawings wherein:

FIG. 1 depicts a plan view partially in cross-section showing animproved electron discharge device utilizing the features of the presentinvention;

FIG. 2 is an enlarged cross-sectional view of a preferred embodiment ofthe present invention taken along the lines 22 of FIG. 1 in thedirection of the arrows;

FIG. 3 is a cross-sectional view of the coupler depicted in FIG. 2 takenalong the lines 33 in the direction of the arrows;

FIG. 4 is a cross-sectional view of a typical prior art Waveguide windowassembly such as shown in U.S. Patent 2,958,834;

FIG. 5 is a fragmentary isometric view of a circular waveguide having acircular wave-permeable vacuumsealed window disposed therein whereinsaid wave-permeable vacuum-sealed window is made of a honeycombstructure;

FIG. 6 is a fragmentary isometric view of a rectangular waveguide havinga wave-permeable honeycomb window disposed in vacuum-sealed relationshiptherein;

FIG. 7 is a cross-sectional view of another wave-permeable vacuum-sealedwindow disposed within a waveguide section, said wave-permeablevacuum-sealed window being made from a honeycomb structure and havingcooling provisions therefore;

FIG. 8 is a fragmentary cross-sectional view of a circ-ular waveguidesection such as depicted in FIG. 4, having a wave-permeablevacuum-sealed window disposed therein wherein said wave-permeablevacuum-sealed window is formed from a composite honeycomb structure;

FIG. 9 is a fragmentary cross-sectional view partially in elevation ofthe wave-permeable window depicted in FIG. 8 take along the lines 99 inthe direction of the arrows;

FIG. 10 is a cross-sectional view partly in elevation of a rectangularwaveguide having a composite honeycomb laminated wave-permeablevacuum-sealed window structure disposed therein;

FIG. 11 is a fragmentary cross-sectional view taken along lines 1111 inthe direction of the arrows of the embodiment depicted in FIG. 10,rotated 90 counterclockwise;

FIG. 12 is a graphical portrayal of aspect ratio versus frequencydepicting the resonant ghost modes found in two typical solid ornon-honeycomb wave-permeable windows cut for resonance at 8 gc. (8000megacycles);

FIG. 13 is a fragmentary cross-sectional view of a coaxial waveguidehaving a honeycomb wave-permeable window vacuum-sealed therein;

FIG. 14 is a fragmentary cross-sectional view of another embodiment ofthe present invention.

Referring now to the drawings and in particular to FIG. 1, there isshown an electron discharge device employing novel features of thepresent invention. A multicavity klystron amplifier tube 13 of the typeshown and described in more detail in US. patent application Ser. No.148,520, filed Oct. 30, 1961, now US. Patent No. 3,281,616, issued Oct.25, 1966, and assigned to the same assignee as the present invention,comprises three main portions: A beam producing section 14 on one endwhich serves to form and project a beam of electrons over apredetermined path directed axially and longitudinally of the tube 13; acentral beam interaction section 15 where interaction takes placebetween the projected electron beam and an applied electromagnetic waveto produce amplification of the wave; and collector structure 16 at theterminating end of the tube 13 where the electrons of the spent beam arecollected. A suitable coolant fluid such as water is applied to thecollector structure 16 via fluid fittings 17 and circulates throughducts (not shown) in the collector structure 16.

The tube 13 is evacuated to a suitable low-pressure, for example, 10torr. Input energy to be amplified is coupled to the upstream end of thebeam interaction section 15 via the intermediary of a rectangularwaveguide 18 and through a vacuum-sealed waveguide structure 19 whichsupports a window sealed therein (not shown) transparent toelectromagnetic waves. Amplified output wave energy is extracted inconventional manner at the downstream end of the beam interactionsection 15 via the intermediary of a rectangular waveguide 20 andthrough an output waveguide window assembly 21 to be described in moredetail below.

Referring now to FIGS. 2 and 3, there is shown an enlarged view of theoutput waveguide assembly 21. A section of circular Waveguide 22 carriestransversely therein a gas-tight wave-permeable window 23 as of, forexample, an alumina type ceramic or any other suitable dielectricmaterial which is both transparent to electromagnetic waves and capableof being sealed in vacuumsealed communication to the inner wall of thecircular guide section 22 such as, for example, A1 0 BeO, fused quartz,single crystal sapphire, boron nitrate, etc. Sealing of thewave-permeable window 23 to the inner wall of circular waveguide 22 maybe made by any of the wellknown sealing techniques, such as, forexample, by brazing.

In a preferred embodiment, the abrupt transition between rectangularwaveguides 20 and circular waveguide 22 are made electrically on theorder of n/ 2 wavelengths apart at the center frequency of the passband,where n can be any positive integer. A structure which is electricallyone wavelength long is defined as one which causes a phase shift of 21rradians in a wave propagating therethrough.

The wave-permeable window 23 disclosed in circular waveguide 22 ispreferably maintained at a minimal thickness in order to preventelectrical breakdown at the window faces due to trapped modes therein.

Referring now to FIG. 4, a typical prior art waveguide window couplerdesign as more thoroughly discussed in US. Patent 2,958,834 is shown.The window assembly 26 depicted in FIG. 4 contains a solidwave-permeable window 27 disposed in a circular waveguide section 28 inthe same fashion as shown in FIGS. 2 and 3. Reference to theaforementioned US. Patent 2,958,834 indicates and further analyticalstudies have shown that it is desirable to minimize the thickness of thewindow 27 in the direction of propagation or to express it another way,maximize the distance between the window faces 27', 27" of thewave-permeable window 27 and the capacitive discontinuities 29 and 30formed by the junction between the circular waveguide 28 and rectangularwaveguide 31 in order to minimize the chances of window failure due tohigh electric field gradients or trapped modes therein. It is known thatthe passband properties of a window such as depicted in FIG. 4 as wellas in FIGS. 2 and 3 is dependent upon the physical thickness of thewindow to a certain degree as well as the dielectric constant of thematerial used in making the window.

The present invention provides an improvement over the prior artconfiguration depicted in FIG. 4 through the utilization of a singularor composite honeycomb type window. Examination of FIGS. 2 and 3 shows aplurality of bores 25 extending partially through the thicknessdimension of window 23 and blanketing the entire crosssectional area ofthe window. The bores 25 can be made such as by drilling, molding, orany other suitable technique for preparing ceramics and dielectrics ofthe aforementioned types. It is to be noted that the distance or axialextent of the bores as taken in the direction of wave propagation ismuch greater than the thickness of the face slab portion 23' which isnecessary to preserve vacuum integrity. It is also to be noted from acomparison of FIGS. 2 and 4 that the thickness L of the composite orhoneycomb structure in FIG. 2 is much greater than the thickness L ofthe solid wave-permeable window de picted in the prior art as shown inFIG. 3. Similarly, the

distance between the face of the slab 23' and the capacitivediscontinuity formed at the junction of the circular and rectangularguides is greater in the embodiment depicted in FIG. 2 than a comparabledistance between the faces 27, 27" of the window 27 and the capacitivediscontinuities in the embodiment of FIG. 4. Thus, it is evident thatthe chances for electrical breakdown between the capacitivediscontinuities in the embodiment of FIG. 2 is much less than in theembodiment of FIG. 4, due to the increased physical separationtherebetween. Furthermore, the field gradients existing in theembodiment of FIG. 2 should be considerably reduced along the length Lof the window in comparison to that of FIG. 4 along the length L of thewindow. Additionally, the window depicted in FIG. 2 being greater inthickness L is obviously of superior strength to the window depicted inFIG. 4. Furthermore, the relationship between the number of bores, thediameter of the bores, spacing between bores and the longitudinal extentof the bores within the window assembly of FIG. 2 can be so varied andinterrelated that the dielectric constant is less in the configurationof FIG. 2 than a window of equivalent strength or even less strengthwhich is solid in nature such as that depicted in FIG. 4. Therefore, itis evident that a stronger window can be made which has a dielectricconstant equivalent to or less than its solid body counterpart such asshown in FIG. 4 through the use of the teachings of the presentinvention.

Theoretical studies have been made of what is termed ghost modes whichare defined as resonant electromagnetic field configurations existing inthe vicinity of certain waveguide obstacles such as dielectric windowsby various people. These modes have been shown to be both of thepropagating and the non-propagating or trapped type. Reference is madeto the following articles: Ghost Modes in Imperfect Waveguides, by E. T.Jaynes, Proceeding of the I.R.E., February 1958, vol. 46, pages 415418.Resonant Modes in Waveguide Windows, by M. P. Forrer and E. T. Jaynes,in I.R.E. Transactions on Microwave Theory and Technique, vol. MIT-8,No. 2, March 1960.

Theoretical and experimental studies have been made on variousdielectric materials and plots of the ghost modes therein have beenmade. Referring to FIG. 12, there is depicted a calculated study showingthe presence of multiple ghost modes in two types of rectangularblocktype windows cut for self-resonance at 8 gc. The characteristics inFIG. 12 depict aspect ratio (A/B) (width/ height) versus frequency. Thesolid lines are indicative of ghost modes found in a /2 wavelength thickresonant block window made from beryllia having a relative dielectricconstant of approximately 6.8 and an aspect ratio of approximately 2.3.The dotted lines are indicative of the ghost modes found in a quartzblock window cut for self-resonance at 8 gc. having a relativedielectric constant of approximately 3.75 and an aspect ratio of 2.3.The physical thickness of the beryllia window was .2925 inch and thephysical thickness of the quartz window was .4050 inch. Examination ofthe ghost modes found in the calculated characteristics depicted in FIG.12 shows that a considerable spreading and shifting of the ghost modesis found when a lower dielectric constant material is employed, eventhough the physical thickness of the window is greater for the lowerdielectric constant material than for the higher dielectric constantmaterial. Thus, it is rather self-evident on examination of FIG. 12 thata window of equal strength but lower dielectric constant than anotherwindow will have characteristics which are considerably more free ofghost mode resonances than the window of higher dielectric constant. Thepresent invention provides a novel solution to such a problem whereinghost mode resonances are deleterious to effective microwavetransmission. Examination in FIG. 12 of the TE mode for the beryllia andfor the quartz windows shows that indeed a definite shift does takeplace in resonant ghost modes regardless of window thickness. Thus, foran alumina, beryllia or any other dielectric constant material, if thedielectric constant can be reduced while simultaneously increasing thephysical thickness of the window then with that particular dielectricconstant material the ghost modes will be shifted up in frequency andspread apart, and a window can easily be constructed to be comparativelymode-free for the passband of interest. Thus, the designer through theutilization of the present invention is given extreme flexibility inpicking modefree bandwidths and designing windows therefore which priorart techniques did not make available. In addition, a window ofincreased strength which has improved thermal and electrical breakdownproperties, thus capable of handling high mul-ti-megawatt powers such ason the order of hundreds of kilowatts average power output or better,can easily be constructed utilizing the techniques of the presentinvention. Quite obviously the techniques of the present invention withregard to reducing dielectric constant while simultaneouslystrengthening a vacuum-sealed wave-permeable window are applicable tothe low energy coupling devices suitable for use in low power tubes aswell as in high power tubes.

The present invention is obviously very broad in nature and applicableto any electromagnetic vacuum-sealed wave transmission system such as,for example, those depicted in FIGS. 5 and 6. In FIG. 5 a circularwaveguide 33 having a circular wave-permeable vacuumsealed window 34therein is shown. The wave-permeable window 34 has a singular type ofhoneycomb structure. FIG. 6 depicts a rectangular waveguide 35 having ahoneycomb type wave-permeable window disposed in vacuum-sealedrelationship therein according to the teachings of the presentinvention. Obviously, the techniques of the present invention withregard to reduction in dielectric constant while simultaneouslyincreasing strength through the use of the honeycomb singular orcomposite window are applicable to coaxial as well as waveguideconfiguration-s.

In FIG. 7, there is depicted another embodiment of a honeycomb type ofwaveguide window structure. A rectangular half-wave length block 37 ofdielectric material as, for example, alumina ceramic is mounted Within arectangular waveguide 38. A series of holes 39 are drilled through block37 to form fluid ducts. Waveguide 38 also contains apertures 40 whichare in alignment with holes 39. The space 41 between housing 42 andwaveguide 38 is adapted to receive a moderately lossy dielectric coolantwhich flows through nozzle 43 in opening 44 through ducts 39 and blocks37, and out through nozzle 45 and opening 46. The fluid is preventedfrom flowing just through the space 41 by means of a pair ofdiametrically opposed septums or fins 47. For a more thoroughexplanation of the cooling techniques see US. patent application Ser.No. 316,865, by Floyd A. Johnson, and assigned to the same assignee asthe present invention, filed Oct. 17, 1963, and copending herewith. Thiscopending application describes cooling techniques which can be used inthe present invention. The holes or bores 39 depicted in the embodimentof FIG. 7 substantially entirely blanket the cross-sectional areas ofthe block window in much the same fashion as depicted in FIGS. 2 and 3,as well as FIGS. 5 and 6. The external fluid circulating means such asfor example, that depicted in my copending US. patent application Ser.No. 316,865 may be utilized to circulate fluid in the embodimentsdepicted in the present invention.

Directing your attention to FIGS. 8 and 9, there is depicted analternative embodiment of the present invention wherein is shown acircular waveguide section 40 fed by a pair of rectangular waveguides 41in much the same fashion as depicted in prior art FIG. 4 and theembodiments of FIGS. 2 and 3. Disposed within and vacuumsealed in thecircular waveguide portion 40 is a wavepermeable composite honeycombtype of waveguide window 42. The wave-permeable window 42 is formed froma composite structure comprising a pair of discs 4-3 and 44 which have ahoneycomb structure 45 sandwiched therebetween. The honeycomb structure45 is characterized by being made from a plurality of hexagonal boresextending completely through the central honeycomb section 45. Anysuitable techniques such as molding or drilling may be utilized to formthe honeycomb section. The composite assembly including the face platesof discs 43' and 44 is preferably sintered together utilizing knowntechniques to form a, practically speaking, integral structure having adielectric constant which is lower than a window made of solid materialwhich is equivalent in thickness. With regard to FIGS. 8 and 9, all theadvantages set forth previously with regard to lowering of thedielectric constant and simultaneously strengthening the window whilephysically increasing the size thereof in order to shift the ghost moderesonances, increase the strength and lessen the chances of thermalstresses rupturing the window as well as reducing the field gradientstherein are applicable to the windows shown in FIGS. 8 and 9.

In FIGS. 10 and 11, an alternative embodiment of the present inventionemploying a laminated composite honeycomb window assembly is depicted.In the embodiments of FIGS. 10 and 11, a honeycomb composite laminatedwave-permeable vacuum-sealed window 46 is depicted in vacuum-sealedrelationshipwithin a rectangular waveguide 49 as shown. The laminatedcomposite honeycomb wave-permeable window is made from a plurality offlat ceramic slabs, discs or plates 47 preferably thin in nature on theorder of less than /s of an electrical wavelength and which havesandwiched therebetween sinuous or corrugated central portions 48forming a honeycomb section between the flat plates 47. Techniquesdescribed in U.S. Patent 3,l12,l84, by R. Z. Hollenbach, mayadvantageously be utilized to form the composite honeycomb windowlaminated structure depicted in FIGS. 10 and 11. The advantages setforth previously with regard to lowering of dielectric constant whilesimultaneously increasing window strength with all the resultantbenefits are equally applicable to the embodiment set forth in FIGS. 10*and 11.

FIG. 13 depicts a coaxial line 50* having a honeycomb coaxial window 51disposed therein in vacuum sealed relationship. All of the previouslymentioned advantages with regard to the utilization of honeycomb windowswith respect to rectangular and circular waveguides are equallyapplicable to the coaxial embodiment depicted in FIG. 13. The window 51can be of any of the previously recited types, composite or singular innature and all of the aforementioned types are equally advantageouslyincorporated in the coaxial embodiments.

The embodiment depicted in FIG. 14 depicts a honeycomb window assembly52 wherein a rectangular waveguide 53 has a honeycomb dielectric window54 disposed therein in vacuum-sealed relationship. The window 54 has acentral solid slab portion 55 as shown and a plurality of bores 56extending inwardly from both faces as shown. The bores may be of thetype described previously with regard to the embodiments depicted inFIGS. 2 and 9, and could even advantageously be formed from thelaminated structure depicted in FIG. 11 with the end slabs 47 removed.The bores 56- are shown as being tapered from the faces of the windowinwardly to the central slab portion 55. This taper concept provides abuilt-in impedance transformation within the window itself to thereforesubstantially reduce reflections of wave energy from the transitionplanes of the window faces and the air or vacuum sides of the window.Quite obviously any known impedance transformation techniques may beadvantageously employed to provide a smooth transition. The embodimentsdepicted in FIGS. 2, and 6 are obviously amendable to the utilization ofthe built-in impedance transformation shown in the embodiment of FIG.14. Furthermore, the embodiments depicted in FIGS.

2, 5, 6' and 14 also enhance the suppression of multipactor effects bycapturing and/ or dispersion of electrons on the apertured windowsurfaces.

With regard to the percentage of voids for a given volume of window, thepresent invention teaches a preferred void/vol. ratio of 50% in all ofthe embodiments, although void/vol. ratios of E1()% can beadvantageously employed without departing from the scope of the presentinvention. With regard to the block window embodiments depicted in FIGS.5, 6 and 7, an electrical thickness of Am and integral multiplesthereof, where x is defined as a 21r radians phase shift of thepropagating energy at the center of the passband of the window, ispreferred although obviously the present invention includes windows ofany dimensions where the honeycomb concept can advantageously beutilized. If air of reduced or atmospheric pressure is trapped withinthe bores, voids, etc., of the honeycomb sections and becomes a problem,pin holes may be drilled or otherwise made interconnecting the voids toa suitable exhaust system for evacuation.

Since, quite obviously, the present invention is broad in nature and theparticular sizes, shapes, orientations, etc., of the voids or bores inthe various embodiments can take innumerable forms, a recitation of samewould be inappropriate. However, the present invention does teach apreferential blanketing of the cross-section area of the window in agiven honeycomb volume with voids, bores, etc., in a more or lesssymmetrical manner. Although obviously differential sized voids, bores,etc., may be utilized as well as random distribution thereof in a givenhoneycomb volume.

Since many changes can be made in the above construction and manyapparently widely different embodiments could be made without departingfrom the scope thereof, it is intended that all matter contained in theabove description or shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A high frequency electromagnetic wave-permeable window assemblycomprising: wave transmission means made of conductive material havingan electromagnetic wave-permeable dielectric self-resonant windowvacuumsealed therein, said wave permeable vacuum-sealed window having ahoneycomb structure, said wave transmission means and said honeycombwindow defining a passband with the center frequency determined at theselfresonant frequency of the window, said window having a thicknessdimension disposed parallel to the direction of wave energy propagationthrough said wave transmission means, said honeycomb structure includinga plurality of bores extending partially through the thickness dimensionof the wave-permeable window.

2. A high frequency electromagnetic wave-permeable window assemblycomprising: wave transmission means made of conductive material havingan electromagnetic wave-permeable dielectric self-resonant windowvacuumsealed therein, said wave-permeable vacuum-sealed window having ahoneycomb structure, said wave transmission means and said honeycombwindow defining a passband with the center frequency determined at theselfresonant frequency of the window, said window having a thicknessdimension disposed parallel to the direction of wave energy propagationthrough said wave transmission means, said wave permeable honeycombwindow having a plurality of bores extending in the direction of wavepropagation through the window, said plurality of bores extendingpartially through the thickness dimension of said window taken along thedirection of wave propagation therethrough, said honeycomb window beingsingular in nature.

3. A high frequency electron discharge device having a predeterminedoperating band in the microwave spectrum including: a vacuum envelope,means for forming and projecting a beam of electrons over an elongatedpredetermined beam path in said envelope, means for collecting the beamat the terminal end of said beam path; electromagnetic interaction meansdisposed within said envelope arranged along said beam path between saidbeam forming and said beam collecting means for electromagneticinteraction with said beam; wave transmission means coupled to saiddevice, said wave transmission means including a dielectricelectromagnetic wavepermeable window vacuum-sealed therein, saiddielectric wave-permeable window having a honeycomb structure, saidhoneycomb dielectric window being self-resonant at a frequency withinthe operating band of said device and having a thickness dimensiondisposed parallel to the direction of wave energy propagation throughsaid Wave transmission means, said honeycomb structure including aplurality of bores extending partially through the thickness dimensionof the wave-permeable window.

4. A high frequency electron discharge device having a predeterminedoperating band in the microwave spectrum including: a vacuum envelope,means for forming and projecting a beam of electrons over an elongatedpredetermined beam path in said envelope, means for collecting the beamat the terminal end of said beam path; electromagnetic interaction meansdisposed within said envelope arranged along said beam path between saidbeam forming and said beam collecting means for electromagneticinteraction With said beam; wave transmission means coupled to saiddevice, said wave transmission means including a dielectricelectromagnetic wavepermeable window vacuum-sealed therein, saiddielectric Wave-permeable window having a honeycomb structure, saidhoneycomb dielectric window being self-resonant at a frequency withinthe operating band of said device and having a thickness dimensiondisposed parallel to the direction of wave energy propagation throughsaid wave transmission means, said wave-permeable honeycomb windowhaving a plurality of bores therein extending in the direction of wavepropagation through the window, said plurality of bores extendingpartially through the thickness dimension of said honeycomb window takenalong the direction of wave propagation through the window, saidhoneycomb Window being single in nature.

References Cited UNITED STATES PATENTS 2,636,125 4/1953 Southworth29155.5 X 2,639,248 5/1953 Overholt 343872 X 2,698,421 12/1954 Kline eta1 33398 X 2,744,042 5/1956 Pace 343872 X 2,783,295 2/1957 Ewing 33398 X2,990,526 6/1961 Shelton 33398 3,221,278 11/1965 Winslow 33398 HERMANKARL SAALBACH, Primary Examiner. ELI LIEBERMAN, Examiner.

P. L. GENSLER, Assistant Examiner.

1. A HIGH FREQUENCY ELECTROMAGNETIC WAVE-PERMEABLE WINDOW ASSEMBLYCOMPRISING: WAVE TRANSMISSION MEANS MADE OF CONDUCTIVE MATERIAL HAVINGAN ELECTROMAGNETIC WAVE-PERMEABLE DIELECTRIC SELF-RESONANT WINDOWVACUUMSEALED THEREIN, SAID WAVE PERMEABLE VACUUM-SEALED WINDOW HAVING AHONEYCOMB STRUCTURE, SAID WAVE TRANSMISSION MEANS AND SAID HONEYCOMBWINDOW DEFINING A PASSBAND WITH THE CENTER FREQUENCY DETERMINED AT THESELFRESONANT FREQUENCY OF THE WINDOW,SAID WINDOW HAVING A THICKNESSDIMENSION DISPOSED PARALLEL TO THE DIRECTION OF WAVE ENERGY PROPAGATIONTHROUGH SAID WAVE TRANSMISSION MEANS, SAID HONEYCOMB STRUCTURE INCLUDINGA PLURALITY OF BORES EXTENDING PARTIALLY THROUGH THE THICKNESS DIMENSIONOF THE WAVE-PERMEABLE WINDOW.